Matrix metalloproteinases (MMPs) constitute a family of genetically related proteolytic enzymes which are capable of cleaving almost all protein constituents of the extracellular matrix. MMPs take part in the extracellular matrix destruction and remodeling in both physiological and pathological conditions, e.g. in wound healing, cancer and metastasis progression, rheumatoid arthritis, periodontitis, etc. (Krane, S. M., Ann. N.Y. Acad. Sci. 732:1-10, 1994, Woessner, J. F. Jr., Ann. N.Y. Acad. Sci. 732:11-21, 1994).
Nine MMPs have been disclosed so far in the literature: fibroblast-type collagenase (MMP-1), 72K gelatinase (MMP-2), stromelysin-1 (MMP-3), putative metalloproteinase-1 (MMP-7), PMN-type collagenase (MMP-8), 92K gelatinase (MMP-9), stromelysin-2 (MMP-10), stromelysin-3 (MMP-11) and macrophage metallo-elastase. Each of the MMP enzymes contains a putative tridentate Zn.sup.2+ -binding site which is believed to constitute the active site in the enzyme (Birkedal-Hansen, H., J. Periodontol. 64:474-484, 1993).
A comprehensive review of the MMPs, their known modes of action, their inhibition by various compounds as well as details of the involvement of MMPs in various pathological conditions and diseases is given in the above mentioned Ann. N.Y. Acad. Sci. 732 and also by Birkedal-Hansen et al. in Crit. Rev. Oral Biol. Med. 4:197-250, 1993, the relevant disclosures of which are incorporated herein by reference.
MMPs and/or their endogenous inhibitors are frequently found in cells, tissue and interstitial fluids, and it is believed that they play an important role in the remodeling of the extracellular matrix. They are associated with rapid cell movements and in the reshaping of the extracellular matrix during growth. Increased amounts of MMPs are expressed also during the invasive growth of primary tumors and metastases, and they seem also to induce expression of MMPs in adjacent stromal cells (DeClerck, Y. A. et al., Ann. N.Y. Acad. Sci. 732:222-231). A link is believed to exist between destruction of joints in rheumatoid arthritis and the expression and action of MMPs and proteolytic cascades related to them (Sorsa, T. et al., Semin. Arth. Rheum. 22:44-53, 1992). Also loosening of hip-prostheses has been shown to involve the expression and action of MMPs, especially MMP-1 (Santavirta et al., Clin. Orthoped. Res. 290:206-215, 1993). MMP-8 seems to be predominant in gingiva, gingival crevicular fluid and saliva in periodontal diseases (Sorsa et al., Ann. N.Y. Acad. Sci. 732:112-131, 1994) and peri-implant sulcular fluid (Ingman et al., J. Clin. Periodontol. 21:301-307, 1994).
There is a variety of other disorders in which extracellular protein degradation plays a prominent role. Examples of such diseases include arthritides, acquired immune deficiency syndrome (AIDS), burns, wounds such as bed sores and varicose ulcers, fractures, trauma, gastric ulceration, skin diseases such as acne and psoriasis, lichenoid lesions, epidermolysis bollosa, aftae (reactive oral ulcer), dental diseases such as periodontal diseases, peri-implantitis, cysts and root canal treatment or endodontic treatment related diseases, etc.
Although MMPs are believed to play a major role in the degradation of interconnective tissues and their components, so far there is little evidence of the specific role and mechanism of the separate enzymes in the biological environment. Since the actual mechanism of the MMPs is not known, finding inhibitors for the various MMPs is based more on experimental testing than on theoretical considerations.
A number of synthetic and natural inhibitors for MMPs have been found and tested for a possible usefulness as described by Vincenti et al. in Arth. Rheum. 37:1115-1126, 1994. Thus, chelating agents and moieties including EDTA, hydroxamate, thiol, phosphonamidate, phosphinate and phosphoramidate groups have been tested (Birkedal-Hansen et al. Crit. Rev. Oral Biol. Med. 4:197-250, 1993). Various sulfur-based inhibitors have also been tested but no very good results have been obtained (Vincenti et al. Arth. Rheum. 37:1115-1126, 1994). Tetracyclines have been found to inhibit MMPs, especially MMP-8 although the inhibition mechanism is not known (Golub et al., Curr. Op. Dent. 2:80-87, 1992; Suomalainen et al., Antimicrobial, Agents & Chemother. 36:227-229, 1992; Sorsa et al., Ann. N.Y. Acad. Sci. 732:112-131, 1994; Lauhio et al., Clin. Exp. Immunol. 98:21-28, 1994)
As disclosed for instance in the above mentioned Ann. N.Y. Acad. Sci. 732, it is envisaged that specific inhibitors could be produced by polyclonal and monoclonal antibodies to various MMP-enzymes. .alpha.-Macroglobulins are also known to inactivate susceptible proteinases and may function as MMP inhibitors. Tissue inhibitors of metalloproteinases (TIMPs) are known to inhibit the activity of the active forms of MMPs.
Although the above discussion shows that inhibitors for MMPs do exist and have been investigated, the tests are still mostly at the experimentation stage and no clinically acceptable inhibitor for MMPs exists as a therapeutic or prophylactic drug for any of the pathological states and diseases potentially connected with MMPs. Adverse side effects, which have been detected in the above described MMP inhibitors include, for instance, toxicities (synthetic peptides), antimicrobial activities (tetracyclines), etc.
While the MMP-dependent reactions provide the mechanism for at least one of the key pathways by which the structural macromolecules of interstitial connective tissues are degraded, it is to be observed that mineralized matrices are believed to be degraded by a totally different reaction mechanism. This is the osteoclastic pathway which is based, at least in part, on a release of acidic thiol proteinases to a specific area on the mineralized matrix surface.
Bisphosphonates constitute a group of compounds known to have an effect on the mineralized matrices of the body. Bisphosphonates are compounds characterized by a P-C-P bond. Several bisphosphonates have been investigated in humans and animals with respect to their effect on bone and bone derived cells. They are especially known for their ability to inhibit bone resorption (Fleisch, H., Drugs 42:919-944, 1991).
No effect of bisphosphonates on other tissues than bone has been reported. Despite the fact that bisphosphonates have been studied on human neutrophil myeloperoxidase (Kawolick et al., Arch. Oral Biol. 35:2015-2035, 1990), on enzymes capable of producing reactive oxygen species and on non-specific hydroxylases and acidic serine proteinases (Felix et al., Biochem. Biophys. Arch. 429:429-438, 1979), no effects of bisphosphonates on collagenase, gelatinase or other MMP activities have been noted. In a round table discussion reported in said Ann. N.Y. Acad. Sci. 732: 273-279, 1994, bisphosphonates are mentioned only in connection with bone resorption and osteoclasts. The effects of bisphosphonates on matrix metalloproteinases participating in connective tissue protein matrix destruction has until now been unknown.